Free will is a complicated philosophical subject, but new research suggests mammals may have it.

It's a question that has been debated by philosophers for millennia: Does free will exist, or are all of our actions and choices determined? Many philosophers believe the answer to this question lies at the heart of moral responsibility (i.e., how can we be responsible for our actions without free will?), so it's also a subject important to religious scholars and law theorists, not to mention psychologists, cognitive scientists and artificial intelligence researchers.

So far most of the science pertaining to the question of free will has bred skepticism about the concept. For instance, a landmark 1983 study by neuroscientist Benjamin Libet found, using EEG, that a certain pattern of brain activity called a "readiness potential" occurs in the human brain just before "spontaneous" actions occur. In other words, Libet's findings present evidence against free will — unconscious or subconscious brain processes make all of our decisions, and the sense that our conscious mind makes the decision is just an illusion.

But a new study, performed on lab rats and conducted by researchers from Portugal’s Champalimaud Centre for the Unknown, could reopen the whole subject for debate. Researchers found evidence that neural readiness potential may not determine a decision, reports Discover. Rather, the readiness potential identified by Libet may actually be a mere contributor to a decision that only happens later, leaving room for the possibility of free will.

For the study, lead researcher Masayoshi Murakami and colleagues trained rats to perform a task requiring patience. Rats were required to wait in place after hearing a sound until a second sound was heard. If they showed patience and completed the task, they were awarded with a larger bowl of water. Researchers monitored the brain activity of the rats during this process using tiny electrodes implanted in their premotor cortexes.

Murakami et al. noticed certain neurons that seemed to be acting as "integrators" (i.e., counters). As the rats waited, the firing activity of these neurons gradually increased. When a rat lost patience and "spontaneously" decided to move toward a smaller reward, this firing activity could be measured as reaching a threshold. The neurons did not always reach this threshold at the same pace, however. Sometimes the integrators counted more quickly, indicating increased impatience. Other times, they would count slower. Why?

The researchers looked deeper, and found a second class of neurons that, interestingly, had a random rate of firing which could predict the rate at which the integrators "counted up." In other words, it appeared that this second class of neurons were providing input to the neural integrators. And it was when the overall input reached a threshold that a "spontaneous" action was triggered.

So what does this have to do with free will? Remember Libet and his experiment? Murakami and colleagues wondered if Libet's readiness potential might be the equivalent of the rat "integrator." If so, then the readiness potential may not be indicative of a pre-determined decision, but rather a mere contributor to a decision that only happens later. The researchers concluded that the integrator threshold might even reflect a sort of boundary between unconscious and conscious neural processes.

Whether or not this leaves adequate room for free will is still an open, and highly philosophical, question. But at the very least, this study certainly promises to muddy the water on the issue.